The present invention is related generally to the art of confidential viewing of video displays, and more particularly to an apparatus and method for altering a fundamental display image to generate a compound substantially featureless image which can be decoded for confidential viewing of the fundamental image only by the intended viewer.
With the increasing use of video displays for a variety of systems, such as those used in desktop computers, laptop computers, televisions, and personal video entertainment systems, there exists an increasing need and desire to provide confidential viewing of these displays by only those who the displayed content is intended for, thus eliminating the possibility of unauthorized viewing.
Various devices have been introduced over the years to prevent unauthorized viewing of video displays. The simplest devices generally include a form of “anti-glare” privacy screen and/or hoods and shields commonly found on desktop computer displays which are intended to restrict viewing to only those who are more or less directly in front of the display. While these are somewhat effective, they cannot prevent viewing by someone peering over ones shoulder, and thus are far from secure.
U.S. Pat. No. 5,488,496, issued Jan. 30, 1996, discusses the removal of the top polarizing layer of an LCD screen. This renders the display “invisible” except to those wearing polarized glasses. However, this system is hardly secure, as anyone can obtain polarized glasses, even ordinary Polaroid glasses. Additionally, the screen is not easily converted between confidential and normal viewing modes, and is only applicable to LCD screens.
IBM has also addressed this issue in four recent patents. U.S. Pat. No. 5,537,476, issued on Jul. 16, 1996, provides secure viewing of a display by utilizing a second set of “primary” colors, which are wavelength-shifted from those used to generate the fundamental image. When combined with the fundamental image in correct proportions, the resulting composite image masks the fundamental image. Secure viewing is provided by viewing the composite image through specially formulated narrow-band filtered glasses, which block the second set of primaries, allowing the fundamental set to pass. However, this approach has many drawbacks: 1) it requires two sets of separate narrow-band color primaries which are wavelength-shifted and do not significantly overlap in their spectrums; 2) a single video display containing pixels of two sets of wavelength-shifted primary colors does not commonly exist and, if so, would require twice as many pixels to maintain the same effective resolution as a single primary set display; 3) to align or overlay two separate video displays, perhaps through the use of a beam splitter as discussed in the patent, would not be an economical solution and would suffer greatly from parallax errors; 4) the viewing glasses require three narrow-band and accurately placed spectral notch filters to block the second set of wavelength-shifted primary colors; and 5) anyone wearing glasses of the proper filter arrangement may still view the fundamental display.
U.S. Pat. No. 5,614,920, issued on Mar. 25, 1997, utilizes a flashing screen of light placed between the video display and the viewer to obscure the fundamental image. Confidential viewing is provided by means of LCD shutters which are time synchronized to block the pulses of light and permit viewing of the fundamental image. However, this approach requires the use of an additional optical light screen, requiring additional power and potentially being distracting or annoying to those in the vicinity of the display not wearing the shutter glasses.
U.S. Pat. No. 5,619,219, issued on Apr. 8, 1997, is similar to both previous IBM patents. This patent suggests the introduction of a secondary wavelength-shifted optical light screen mask between the video display and the viewer. The light masking source utilized is intended to be narrow in its spectra, and not conflicting or interfering with the primary colors of the fundamental display image, so that narrow-band filtered glasses may absorb, or block, the wavelength-shifted light, allowing the fundamental image to pass. This approach has many of the inherent limitations of both the prior two patents.
U.S. Pat. No. 5,801,697, issued on Sep. 1, 1998, is essentially a software application which allows selective shielding of various areas of the display, to cover or hide confidential information. There is no viewing means for full screen confidential viewing, and it provides only slightly greater security than that inherent to Microsoft Windows, i.e., simply reducing the window size to hide sensitive information.
Sun Microsystems has also addressed the need for confidential viewing in U.S. Pat. No. 5,629,984, issued May 13, 1997. In this patent, the use of pre-set video flash frames is suggested, which are intended to prevent an unauthorized person not wearing appropriate shutter glasses from intelligibly reading the video display by influencing the person's eye prior to displaying the video data frame. Similar to U.S. Pat. No. 5,614,920, this patent suggests the use of a predetermined obscuring “flash” which has no relation to the fundamental image. While this approach may obscure the image, the overall image will be far from featureless, and potentially annoying to those not wearing the appropriate eyewear.
Intel Corporation has also visited this subject in U.S. Pat. No. 5,963,371, issued on Oct. 5, 1999. In this patent, a method is described for displaying private data to collocated users of the same display, all of whom are required to wear appropriate eyewear. Privacy for a single user may also be obtained by alternating the desired data with that of masking data, where the mask pattern is either a static, predetermined pattern, or a random pattern of black and white pixels, unrelated to the fundamental image, designed to obscure the corresponding areas of the opposite image. This approach is entirely inadequate for the masking of images. It does not provide for a featureless image, and is not suitable for real-time full motion video.
In addition to the above, Shin Ohtake and Yoshinao Aoki, of Japan, published results of their experiments on masking text characters of a CRT display in 1990. Character masking was achieved by synchronously displaying multiple text screens of primary text font characters and experimentally-determined masking font characters. Confidential viewing was provided by viewing the display through LCD shutter glasses synchronized to block the masking fonts. This approach proved to be somewhat successful for text, but does not lend itself to full color graphics or images.
Similar to Ohtake and Aoki, Sony addressed this topic in Japanese Patent No. 05119754 JP, filed in 1991 and published in 1993. This patent discusses alternating a display object screen with a complementary color screen. However, as it will be pointed out later with more detail, an image when mixed with its color complement rather than its color inverse will not necessarily result in a featureless image.
Toshiba, in Japanese Patent No. 01032332 JP published in 1989, discloses the extension of 3-Dimensional viewing applications to that of screen security. They propose that by separating the image to the left and right perspective views, that the combined image is blurred and security is enhanced. Viewing the image through synchronized glasses clears the image as well as providing for 3-dimensional viewing. In practice however, the features of the combined image, while blurred somewhat, are highly distinguishable.
Finally, head-mounted displays are becoming ever more popular, but are expensive and do not facilitate easy viewing of your surroundings or computer keyboard.
Therefore, given the desire and need for a simple, low cost, and effective means of display security, and the limitations of the prior art, it is apparent that a better means is necessary for providing confidential viewing of a standard video display, which does not require cumbersome, cost-intensive supplemental and/or wavelength-shifted masking light sources, and which can be used in all applications of full color/full motion graphics and images.
It is believed that my image altering apparatus and method as described hereafter accomplishes this end while minimizing the cost of implementation and greatly enhancing the viewing security of video displays today.